$z-layers: ( "submit-box": 10, "disable-panes": 5, "write-extra": 6, "write-header": 15, "modal": 100, "modal-content": 110, "upload-mask": 120, "user-menu": 10, );
@function z($layer) {
  @if not map-has-key($z-layers, $layer) {
    @warn "No layer found for `#{$layer}` in $z-layers map. Property omitted.";
  }
  @return map-get($z-layers, $layer);
}